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Increase ADC resolution for FYSETC S6, STM32 #20519

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Dec 22, 2020
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Increase ADC resolution for FYSETC S6, STM32 #20519

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6 changes: 3 additions & 3 deletions Marlin/src/HAL/STM32/HAL.h
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Original file line number Diff line number Diff line change
Expand Up @@ -159,14 +159,14 @@ static inline int freeMemory() {

#define HAL_ANALOG_SELECT(pin) pinMode(pin, INPUT)

inline void HAL_adc_init() {}

#define HAL_ADC_VREF 3.3
#define HAL_ADC_RESOLUTION 10
#define HAL_ADC_RESOLUTION ADC_RESOLUTION // 12
#define HAL_START_ADC(pin) HAL_adc_start_conversion(pin)
#define HAL_READ_ADC() HAL_adc_result
#define HAL_ADC_READY() true

inline void HAL_adc_init() { analogReadResolution(HAL_ADC_RESOLUTION); }

void HAL_adc_start_conversion(const uint8_t adc_pin);

uint16_t HAL_adc_get_result();
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2 changes: 2 additions & 0 deletions Marlin/src/module/thermistor/thermistors.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,8 @@
#define THERMISTOR_TABLE_SCALE (HAL_ADC_RANGE / _BV(THERMISTOR_TABLE_ADC_RESOLUTION))
#if ENABLED(HAL_ADC_FILTERED)
#define OVERSAMPLENR 1
#elif HAL_ADC_RESOLUTION > 10
#define OVERSAMPLENR (20 - HAL_ADC_RESOLUTION)
#else
#define OVERSAMPLENR 16
#endif
Comment on lines +30 to 34
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What does this change achieve. I'm not doubting it, Is this simply because fewer samples are needed to generate an averaged reading when using the higher resolution?

Is the number choice here arbitrary?

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In fact, this is a crutch so as not to change the existing oversampling mechanism. All measurements are summed in a 16-bit field, so a high ADC bit depth simultaneously with a large oversampling ratio will cause an overflow.
A few lines below there is a static validation for this (MAX_RAW_THERMISTOR_VALUE).

Since there is no easy way to transfer OVERSAMPLENR from hal (well, at least there are doubts that this needs to be introduced), I preferred to calculate it automatically for high-bit ADCs to avoid overflow. There is, of course, an opportunity to set HAL_ADC_FILTERED at the hal level, which will completely disable oversampling, but this is semantically incorrect, since no filtration is performed in this hal.

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Works for me. The main thing is to have at least some number of oversamples to deal with the natural variation in ADC readings. Guaranteed to be over 10 is reasonable.

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2 changes: 2 additions & 0 deletions buildroot/share/PlatformIO/variants/MARLIN_FYSETC_S6/variant.h
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Expand Up @@ -114,6 +114,8 @@ extern "C" {
#define NUM_ANALOG_INPUTS 7
#define NUM_ANALOG_FIRST 80

#define ADC_RESOLUTION 12

// PWM resolution
// #define PWM_RESOLUTION 12
#define PWM_FREQUENCY 20000 // >= 20 Khz => inaudible noise for fans
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